Fuel cells are electrochemical cells in which a free energy change resulting from a fuel oxidation reaction is converted into electrical energy. Applications for fuel cells include battery replacement, mini- and microelectronics, automotive engines and other transportation power generators, power plants, and many others. One advantage of fuel cells is that they are substantially pollution-free.
In hydrogen fuel cells, hydrogen gas is oxidized to form water, with a useful electrical current produced as a byproduct of the oxidation reaction. A solid polymer membrane electrolyte layer can be employed to separate the hydrogen fuel from the oxygen. The anode and cathode are arranged on opposite faces of the membrane. Electron flow along the electrical connection between the anode and the cathode provides electrical power to load(s) interposed in circuit with the electrical connection between the anode and the cathode. Hydrogen fuel cells are impractical for many applications, however, because of difficulties related to storing and handling hydrogen gas.
Organic fuel cells may prove useful in many applications as an alternative to hydrogen fuel cells. In an organic fuel cell, an organic fuel such as methanol is oxidized to carbon dioxide at an anode, while air or oxygen is simultaneously reduced to water at a cathode. One advantage over hydrogen fuel cells is that organic/air fuel cells can be operated with a liquid organic fuel. This diminishes or eliminates problems associated with hydrogen gas handling and storage. Some organic fuel cells require initial conversion of the organic fuel to hydrogen gas by a reformer. These are referred to as “indirect” fuel cells. The need for a reformer increases cell size, cost, complexity, and start up time. Other types of organic fuel cells, called “direct,” eliminate these disadvantages by directly oxidizing the organic fuel without conversion to hydrogen gas. To date, fuels employed in direct organic fuel cell development methanol and other alcohols, as well as formic acid and other simple acids.
Conventional direct fuel cells have unresolved problems related to the electro-oxidation reaction promoted by the anode. For example, an intermediate produced during the oxidation/reduction reaction in the existing fuel cells is poisonous carbon monoxide gas. Hazards are thus presented. Also, CO is known to poison catalysts. especially platinum (Pt) based catalysts and to thereby decrease cell efficiency.
Other metals or metal combinations have been employed as anode catalysts, such as platinum-palladium (PtPd) and platinum-ruthenium (PtRu). These combinations, however, have not solved the problem of CO poisoning the catalysts.
A further problem is that power levels in direct organic fuel cells have not previously been sufficient to run many commonly-used devices.
The present fuel cells, which employ palladium-based electrocatalysts, overcome one or more of these and other problems unresolved in the field.